I think there data on Cost of Living is outdated, specifically as it regards Seattle, which has recently seen a significant increase in COL. According to their calculations Seattle is cheaper than DC, however the data I can find online suggests the opposite.
That helps explain it, thank you. It looks like the root problem is they are using the (excl rent) number, and the recent increase in COL is Seattle has been driven by real estate, so the problem isn't there data, it's how they are applying it.
http://www.bestplaces.net/cost-of-living/seattle-wa/washingt...